Overview and Objectives:
Mississippi has a broad spectrum of soils making up its landscape. It is one
of the few states that contains as many as eight of the twelve soil orders.
This contributes to the high amount of variability seen throughout its
soils. Many studies have shown the importance of soil physical and chemical
properties on the variation in soil characteristics and that found that soil
physical and chemical properties have the potential to vary significantly
with landscape position. However, a lack of consistent correlation between
soil variables and yield is not uncommon. The soil factor that may affect
yield in one area within a field is subject to change throughout the field
hence, its influence on yield can change. As new precision agricultural
technologies reach the public, there is a great deal of question as to the
abilities of these technologies. Without a thorough understanding of the
factors affecting soybean production, it is impossible to determine the
benefits of these technologies. This study attempts to define the benefits
of precision agriculture to soybean production in Mississippi. Specific
To determine the
amount of variability in selected soil physical and chemical properties.
To determine the
effect soil variability on soybean yield.
To determine if
soil variability could be described by soil series.
To determine if
apparent soil electrical conductivity could be related to soil properties.
To determine if changes in apparent soil electrical conductivity could be
related to changes in soybean yield.
Results To Date:
Delta and Hill (Producer) Fields:
Variability of the measured soil
parameters range from low (pH) to quite high (P) within the three fields
used in this study. However, the variability of chemical factors tend to
follow the same order among the fields suggesting that this order was
somewhat common. Linearity among the soil parameters made their correlation
with yield difficult to interpret. Principle component analysis coupled with
stepwise regression allowed us to speculate that general fertility, clay
content, and topography had important influences on crop yield with
topography and clay content having an influence in all three fields.
Although the influence of these factors are not always straightforward, the
specific influence of the topographic features and clay content appeared to
vary between fields and years and seemed to indicate water flow in the
fields. While the topographic factors and clay content helped explain yield
variation, they would be of questionable value in planning SSSM prior to the
growing season. The principle component analysis also revealed some factor,
possibly associated with P and K, that reduced crop yield. This factor
requires more investigation as to its identity. As these three fields were
considered representative of common Mississippi fields, the topographical
and soil texture features of production fields should be considered when
defining soil management.
In addition to using the soil properties and topography to delineate
management zones, comparisons of soil properties to soil series were also
attempted. Only one field showed relationships between soil series and
topography. There was no relation between yield and soil series for any of
the three fields. These results indicate that using soil series as a
delineating factor for soil management zones will lead to erroneous
Black Belt (Experiment Station) Fields:
The three fields chosen for this
study possessed different histories and yield and soil characteristics
despite a close proximity to each other. Two of the three fields had medium
to high P and K values but low yields while the third field had low P and K
values but relatively higher yields. These relationships suggest that soil
factors other than fertility were yield-affecting. Soil variability, with
the exception of pH, was highest in the North field. Potassium in this field
exhibited evidence of high amounts of small-scale variability with CV’s
increasing approximately 66% despite soil samples being collected from the
same areas. A lack of correlation between elevation and other soil
properties indicated that negligible amounts of erosion had taken place in
this field. The South and East fields used in this study had evidence of
erosion processes taking place, however, this evidence was strongest for the
East field. In the other measured soil factors, variability in these two
fields were similar. Principle component analysis coupled with stepwise
regression revealed that soil pedogenic factors (parent material,
topography, and texture) influenced soybean yield more consistently across
all three fields than any of the other measured soil properties. However,
the effects of topography and texture appear to change based on the climatic
conditions experienced by the crop during the growing season. This is
interpreted to mean that these two factors were more indicative of the water
holding characteristics of these fields. Soil fertility parameters did not
appear to have much effect on soybean yield in these three fields. These
results suggest that using pedogenic soil factors to determine soil
management zones would be more beneficial than using anthropogenic factors
such as soil fertility.
As many factors influence yield, and the objective of this project is to
determine if EC can be used to define soil management zones, EC was also
related to soil properties using the same methods as with. In the north
field, shallow EC (0 to 1 ft) appeared to be related negatively to silt
content and positively to elevation and slope while the deep EC appeared to
be negatively related to silt and positively to slope. In the south field,
shallow EC appeared related to P and K, and negatively related to clay
content. Deep EC appeared to be related to Mg and elevation. In the east
field, the relationship between EC and soil properties appeared to be much
more involved. Shallow EC appeared to be related to texture, Ca, K, and Mg.
Deep EC appeared to be related to silt, K, and Mg.
Conclusions To Date:
Research indicates that many factors are influencing soybean yield in these
fields. It appears that soil management zones cannot be strictly determined
using any one soil parameter across all three fields. In these fields, it
appears that topography and soil texture, most likely as they relate to
plant available water, would be parameters that could be used on all fields.
However, these parameters would not meet all of the needs on any of the
fields used in this study. Main management zones based on these soil
properties could then be further defined, possibly based on soil test
It also appears that soil series difference will not adequately serve to
delineate soil management zones. This could be due to many factors
influencing soil mapping decisions.
Differences in soil series within fields may be due to subsoil
characteristics that do not influence surface soil or yield parameters, or
to differences in surface soil characteristics being removed due to
anthropogenic reasons as the cropping histories of fields lengthen.
soil EC as a method for delineating soil management zones.
include hydrologic modeling moisture patterns in the field.
remote sensing as method for delineating management zones.
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